The following describes a conventional DVD-Video disc (hereinafter referred to as a “DVD”).
FIG. 1 is a diagram showing the structure of a DVD. As is shown in the bottom of FIG. 1, the DVD includes a logical address space in between the read-in area and the read-out area. In the logical address space, volume information of the file system is stored at the top, and application data such as video and audio is stored in the subsequent areas.
The file system of a DVD is a file system compliant with ISO9660 and the Universal Disc Format (UDF). File system is a mechanism for representing data on a disc by units called directories and files. In a personal computer (PC), a file system called FAT or NTFS is used. Such a file system allows a computer to process data stored in the hard disk in the form of directories and files. As a result, usability is enhanced.
Both UDF and ISO9660 are used in DVDs as their file systems. UDF and ISO9660 are sometimes referred to collectively as “UDF Bridge”. Data stored on a DVD can be read out by the file system driver of either UDF or ISO9660. In the case of DVD-RAM/R/RW, which are rewritable DVDs, data reading, writing, and deletion are physically possible.
Data stored on a DVD exists as directories or files as shown in the upper left of FIG. 1 via the file system. Immediately below the root directory (“ROOT” in FIG. 1), a directory called “VIDEO_TS” is placed, where application data of the DVD is stored. The application data is divided and stored as plural files. The following are some of the major files:
VIDEO_TS. IFOdisc reproduction control information fileVTS_01_0. IFOvideo title set#1 reproduction controlinformation fileVTS_01_0. VOBvideo title set#1 stream file. . .
There are two extensions specified. “IFO” is an extension indicating that a file with this extension stores reproduction control information. “VOB” is an extension indicating that a file with this extension stores an MPEG stream being AV data. The reproduction control information is information that includes information for realizing interactivity (technique for dynamically changing the state of reproduction according to a user operation) employed for the DVD as well as information, such as meta data, which is attached to a title or an AV stream. The reproduction control information of the DVD is called navigation information in general.
The reproduction control information files include “VIDEO_TS. IFO” intended for the management of the entire disc, and “VTS—01—0. IFO” being the reproduction control information of an individual video title set. “01” in the body of the filename indicates the number of the video title set. In the case where the number of a video title set is #2, for example, the filename of such video title set is “VTS—02—0. IFO”. Note that a single DVD can store plural titles, that is, plural movies with different stories and plural movies with the same story but with different versions.
The upper right of FIG. 1 shows a DVD navigation space in the application layer of the DVD, i.e., a logical structure space where details of the above-described reproduction control information are shown. Details of information in “VIDEO_TS. IFO” are shown in the DVD navigation space as Video Manager Information (VMGI). Details of the reproduction control information which exists for each video title set such as “VTS—01—0. IFO”, are shown in the DVD navigation space as Video Title Set Information (VTSI).
VTSI describes Program Chain Information (PGCI) which is information about a reproduction sequence called a Program Chain (PGC). The PGCI is made up of a group of cells and a kind of programming information called a command. Each cell represents a part or the whole segments in a Video Object (VOB; MPEG stream). The reproduction of a cell means to reproduce segments in a VOB that are specified by such cell.
A command, which is processed by a DVD-capable virtual machine, is similar to Java (registered trademark) Script executed on a browser. Java (registered trademark) Script performs window and browser controls (e.g., opens a new browser window), in addition to logical operations. Meanwhile, a DVD command performs only the reproduction control of AV titles (e.g., the specification of a chapter to be reproduced), in addition to logical operations. This is a difference between a DVD command and Java (registered trademark) Script.
Each cell includes information about the start address and end address (logical storage address on the disc) of a VOB stored on the disc. A player reads out data using such information described in the cell about the start address and end address of the VOB, and reproduces the read data.
FIG. 2 is a diagram for describing the navigation information in the AV stream. Interactivity, which is characteristics to a DVD, is not realized only by the navigation information stored in the above-described “VIDEO_TS. IFO” and “VTS—01—0. IFO”. Several pieces of important information for realizing interactivity are multiplexed in the VOB with video data and audio data, using dedicated carriers called navigation packs (hereinafter referred to as “navi pack(s)” or “NV_PCK”).
Here, a description is given of menu as a simple example of interactivity. Several buttons appear on the menu screen. For each of such buttons, the details of a process to be performed when such button is pressed, are defined. One button is selected on the menu. Highlight, which is a semitransparent image to be overlaid on the selected button, indicates that the button on which it is overlaid is selected. The user can shift to any of the buttons located above, below, right or left of the currently selected button, using the Up/Down/Right/Left key on the remote control. Using the Up/Down/Right/Left key on the remote control, the user moves the highlight to a button corresponding to the process such user wishes to execute, and then presses the Determination key. Accordingly, a program of a command corresponding to such selected button is executed. For example, the reproduction of a title or a chapter is executed by the command (for example, refer to Japanese Laid-Open Patent application No. 09-282848).
The upper left of FIG. 2 shows an overview of the control information stored in NV_PCK.
NV_PCK includes highlight color information and button information of each button. The highlight color information describes color palette information. The color palette information specifies a semitransparent color of a highlight to be overlaid. Each button information describes: rectangular area information that is information about the position of each button; move information indicating a move from one button to another button (specification of a destination button corresponding to a user selection of the Up/Down/Right/Left key on the remote control); and button command information (a command to be executed when such button is selected).
As shown in the upper right center of FIG. 2, a highlight on the menu is generated as an overlay image. The overlay image is an image generated by giving a color specified by the color palette information to a button specified by the rectangular area information in the button information. Such overlay image is displayed on the screen, superimposed on the background image shown in the right of FIG. 2.
The menu display of the DVD is performed in the above-described manner. The reason that a part of the navigation data is in the stream using NV_PCK is to allow the menu information to be dynamically updated in synchronization with the stream. For example, a first reason is to allow the menu to be displayed only for five to ten minutes in the middle of movie reproduction. A second reason is to allow the stream and the menu information to be displayed in synchronization with each other even for application data for which synchronous display of the stream and menu information is difficult. Another major reason is to improve user operability. For example, by storing, in NV_PCK, information for supporting special reproduction, it becomes possible to smoothly decode and reproduce AV data stored on a DVD even when such AV data is reproduced in a special manner such as forward reproduction and rewind reproduction.
FIG. 3 is a conceptual diagram showing a VOB being a DVD stream. Data such as video data, audio data, and subtitle data shown in FIG. 3(A) are each packetized and packed, as shown in FIG. 3(B), based on the MPEG system standard (ISO/IEC13818-1), and multiplexed as shown in FIG. 3(C), to be generated as a single MPEG program stream. NV_PCK including a button command for realizing interactivity is multiplexed together with the packets and packs.
Data multiplexing in the MPEG system is characterized in that, while each data to be multiplexed forms a bit string based on the decoding order, data to be multiplexed, i.e., video data, audio data, and subtitle data are not necessarily arranged in order of reproduction, i.e., decoding order. This is attributable to the fact that a decoder model for MPEG system streams (generally referred to as a “System Target Decoder” or an “STD” (refer to FIG. 3(D))) has decoder buffers corresponding to the respective elementary streams obtained by demultiplexing the multiplexed data, and such demultiplexed data are temporarily stored in the respective decoder buffers until the time of decoding. The size of decoder buffers specified by the DVD-Video standard differs on an elementary stream basis. The size of the buffer for video data is 232 KB, the size of the buffer for audio data is 4 KB, and the size of the buffer for subtitle data is 52 KB.
In other words, the subtitle data that is multiplexed together with the video data is not necessarily decoded or reproduced at the same timing as that at which the video data is decoded and reproduced.